Safety and antitumor activity of metformin plus lanreotide in patients with advanced gastro-intestinal or lung neuroendocrine tumors: the phase Ib trial MetNET2

In retrospective studies, metformin use has been associated with better clinical outcomes in diabetic patients with advanced, well-differentiated neuroendocrine tumors (WDNETs). However, prospective evidence of metformin safety and activity is lacking. Here, we conducted the first-in-human phase Ib MetNET2 trial to investigate the safety and antitumor activity of metformin in combination with the somatostatin analog lanreotide autogel (ATG) in both diabetic and non-diabetic patients with advanced WDNETs of the gastrointestinal (GI) or thoracic tract. Enrolled patients received lanreotide ATG 120 mg plus oral metformin, up to a maximum dosage of 2550 mg/day. We enrolled 20 patients, of whom 18 (90%) and 2 (10%) had WDNETs of the GI and thoracic tract, respectively. Fourteen patients (70%) were non-diabetic. With a 5% incidence of SAEs, the study met its primary objective of demonstrating treatment safety. With a median follow-up of 39 months (95% CI 28-NE), median PFS was 24 months (95% CI 16-NE), with 12-month and 24-month PFS probability of 75% (95% CI 58–97) and 49% (95% CI 31–77), respectively. We found no statistically significant PFS differences between diabetic and non-diabetic patients. Among exploratory analyses, the presence of tumor genomic alterations in DNA damage pathways was associated with trend towards worse PFS, whereas a precocious reduction of HOMA-IR index and plasma cholesterol concentration showed a trend towards an association with better PFS. In conclusion, metformin plus lanreotide ATG is a safe and well tolerated combination treatment that is associated with promising antitumor activity in both non-diabetic and diabetic patients with WDNETs, and that warrants further investigation in larger clinical trials. Supplementary Information The online version contains supplementary material available at 10.1186/s13045-023-01510-9.


To the Editor
Somatostatin analogs (SSAs) are the mainstay of treatment for patients with advanced, well-differentiated NETs (WDNETs) expressing somatostatin receptors [1,2].The antitumor effects of SSAs in WDNETs are in part mediated through the inhibition of the PI3K/AKT/ mTOR and MAPK pathways [3].In retrospective studies, the use of the antidiabetic compound metformin in diabetic patients with advanced WDNETs was associated with better clinical outcomes when combined with standard SSAs plus/minus everolimus [4][5][6][7].However, no prospective evidence exists to support metformin use in combination with SSAs in advanced WDNET patients with or without diabetes mellitus (DM).Based on these premises, we conducted MetNET-2, a first-in-human, phase Ib clinical trial that investigated the safety and antitumor activity of experimental metformin in combination with standard lanreotide autogel (ATG) in both diabetic and non-diabetic patients with advanced GI or thoracic WDNETs.The primary study objective was to assess the safety of the experimental treatment, as defined as the incidence of serious adverse events (SAEs).Study Methods are reported in Additional file 1.
Between April 2016 and April 2019 we enrolled a total number of 20 patients, whose characteristics are summarized in Additional file 2: Table S1.Of these, six patients (30%) had a prior diagnosis of DM.Median duration of exposure to the experimental treatment was 15.9 months (IQR range, 5.8-21.0).Study drug exposure is reported in Additional file 3: Fig. S1 and Additional file 4: Table S2.With only one treatment-related SAE (5%, acute renal failure), MetNET-2 met its primary endpoint demonstrating the safety of metformin plus SSAs.The renal SAE was likely to be multifactorial (G2 hypertension NDR, G1 urolithiasis NDR), with a possible contribution of metformin-related pre-renal kidney injury from G1 diarrhea.Of note, this toxicity was reversible after temporary interruption of metformin administration and the initiation of antihypertensive therapy.The most common any-grade treatment-related AEs (trAEs) were diarrhea (75%), hyperglycaemia (55%), asthenia (40%) and hypercholesterolemia (40%) (Table 1).Grade 3 trAEs occurred in 15% of patients, and consisted of acute renal failure (n = 1; 5%), diarrhea (n = 1; 5%) and abdominal pain (n = 1; 5%).No grade ≥ 4 trAEs were reported.trAE incidence was not significantly different in diabetic versus non-diabetic patients (Additional file 5: Table S3).
In addition, no trAEs led to the discontinuation of Lanreotide ATG or metformin.Treatment-emergent AEs are reported in Additional file 6: Table S4.
In the whole 24 months follow-up period, we observed no significant changes in any of the metabolic parameters evaluated (Fig. 1C-H; Additional file 15: Table S8).The HOMA-IR index was reduced 3 months after treatment initiation, whereas patient BMI and plasma cholesterol levels were reduced within 6 months (Fig. 1C-H; Additional file 15: Table S8).Patients experiencing higher early reduction of HOMA-IR index and plasma cholesterol concentration showed a trend towards better PFS (p = 0.055 and p = 0.086, respectively, Additional file 16: Table S9).In conclusion, metformin plus lanreotide ATG is safe, well tolerated and active in both non-diabetic and diabetic patients with WDNETs of the GI or thoracic tract.A precocious reduction of HOMA-IR index and plasma cholesterol may predict higher clinical benefit from this treatment.Larger, prospective clinical trials should be conducted to investigate if adding metformin to SSAs results in outcome improvement when compared to SSAs alone in this clinical setting.

Fig. 1
Fig. 1 Kaplan-Meier curves for progression-free survival (PFS) (A) and time-to-progression (TTP) in the MetNET2 study cohort (B).Box plots depicting changes in the indicated metabolic parameters during the experimental treatment (C-H).The p value in panels C-H refers to the paired t test for the indicated comparisons

Table 1
Most common treatment-related adverse events (trAEs)